KSZ8995MA B3 Micrel Inc, KSZ8995MA B3 Datasheet - Page 24

• Manufacturer Part Number: KSZ8995MA B3
• Manufacturer: Micrel Inc

Specifications of KSZ8995MA B3

• Number Of Primary Switch Ports: 5
• Internal Memory Buffer Size: 64
• Operating Supply Voltage (typ): 1.8/2.5/3.3V
• Fiber Support: Yes
• Integrated Led Drivers: Yes
• Phy/transceiver Interface: MII/SNI
• Power Supply Type: Analog/Digital
• Package Type: PQFP
• Data Rate (typ): 10/100Mbps
• Vlan Support: Yes
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Pin Count: 128
• Mounting: Surface Mount
• Jtag Support: No
• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Compliant

Micrel, Inc.
KS8995MA/FQ
Scrambler/De-Scrambler (100BASE-TX only)
The purpose of the scrambler is to spread the power spectrum of the signal in order to reduce EMI and baseline
wander. The data is scrambled through the use of an 11-bit wide linear feedback shift register (LFSR). This can
generate a 2047-bit non-repetitive sequence. The receiver will then de-scramble the incoming data stream with the
same sequence at the transmitter.
100BASE-FX Operation
100BASE-FX operation is very similar to 100BASE-TX operation except that the scrambler/de-scrambler and MLT3
encoder/decoder are bypassed on transmission and reception. In this mode the auto-negotiation feature is bypassed
since there is no standard that supports fiber auto-negotiation.
100BASE-FX Signal Detection
The physical port runs in 100BASE-FX mode if FXSDx >0.6V for ports 3, 4 (KSZ8995FQ) or ports 4, 5 (KSZ8995MA)
only. This signal is internally referenced to 1.25V. The fiber module interface should be set by a voltage divider such
that FXSDx ‘H’ is above this 1.25V reference, indicating signal detect, and FXSDx ‘L’ is below the 1.25V reference to
indicate no signal. When FXSDx is below 0.6V then 100BASE-FX mode is disabled. Since there is no auto-
negotiation for 100BASE-FX mode, the ports must be forced to either full or half-duplex for the fiber ports. Note that
strap-in options exist to set duplex mode for port 4, but not for port 3, 5.
100BASE-FX far End fault
far end fault occurs when the signal detection is logically false from the receive fiber module. When this occurs, the
transmission side signals the other end of the link by sending 84 1s followed by a zero in the idle period between
frames. The far end fault may be disabled through register settings.
10BASE-T Transmit
The output 10BASE-T driver is incorporated into the 100BASE-T driver to allow transmission with the same
magnetics. They are internally wave-shaped and pre-emphasized into outputs with a typical 2.3V amplitude. The
harmonic contents are at least 27dB below the fundamental when driven by an all-ones Manchester-encoded signal.
10BASE-T Receive
On the receive side, input buffer and level detecting squelch circuits are employed. A differential input receiver circuit
and a PLL perform the decoding function. The Manchester-encoded data stream is separated into clock signal and
NRZ data. A squelch circuit rejects signals with levels less than 400mV or with short pulsewidths in order to prevent
noises at the RXP or RXM input from falsely triggering the decoder. When the input exceeds the squelch limit, the
PLL locks onto the incoming signal and the KS8995MA/FQ decodes a data frame. The receiver clock is maintained
active during idle periods in between data reception.
Power Management
The KS8995MA/FQ features a per port power down mode. To save power the user can power down ports that are
not in use by setting port control registers or MII control registers. In addition, it also supports full chip power down
mode. When activated, the entire chip will be shutdown.
MDI/MDI-X Auto Crossover
The KS8995MA/FQ supports MDI/MDI-X auto crossover. This facilitates the use of either a straight connection CAT-
5 cable or a crossover CAT-5 cable. The auto-sense function will detect remote transmit and receive pairs, and
correctly assign the transmit and receive pairs from the Micrel device. This can be highly useful when end users are
unaware of cable types and can also save on an additional uplink configuration connection. The auto crossover
feature may be disabled through the port control registers.
Auto-Negotiation
The KS8995MA/FQ conforms to the auto-negotiation protocol as described by the 802.3 committee. Auto-negotiation
allows unshielded twisted pair (UTP) link partners to select the best common mode of operation. In auto-negotiation
the link partners advertise capabilities across the link to each other. If auto-negotiation is not supported or the link
partner to the KS8995MA/FQ is forced to bypass auto-negotiation, then the mode is set by observing the signal at
the receiver. This is known as parallel mode because while the transmitter is sending auto-negotiation
24
Semptember 2008
M9999-091508